This invention relates to a steam distribution device for a steam humidifier system.
Humidification may be accomplished by a variety of techniques, such as spraying finely atomized water into the atmosphere, by employing evaporative belts that are continuously moistened by water and which are presented to an air flow path, and by direct steam injection.
Steam injection is undoubtedly the most efficient humidification system in situations requiring very large quantities of vapor to be discharged and particularly for industrial humidification. Steam injection systems, however, must be properly designed, since humidification by wet steam is accompanied by water droplets emerging from the unit, thus wetting ducts, ceilings, floors, and surrounding equipment.
Steam humidification is usually accomplished by conducting steam through a pipe having perforations and into the atmosphere to be humidified. If wet steam emerges from the perforations, drip pans are provided to collect the water. A more desirable technique is to minimize the emergence of wet steam from the perforations.
There are generally speaking two methods to accomplish this. In the first method, the perforated steam dispersion tube is surrounded by a heated jacket so that the steam dispersion tube is already hot at the time the humidistat calls for steam. Because the dispersion tube is at or close to steam temperature, little condensation is produced when live steam enters the dispersion tube.
A problem with this type of system is that the pre-heated jacket causes the owner to incur extra costs for air conditioning, since air conditioning systems are frequently run at the same time as humidification systems.
To avoid the extra air conditioning costs imposed by a pre-heated jacket system, cold tube systems have been used. In these systems, the challenge is to find a means of getting rid of condensate from the unjacketed cooled tube or tubes without condensate being carried with the steam into the duct or air handler. A single wall tube with no buffer from the cool airstream will create much more condensate. Condensate creation consumes BTUs that are wasted.
Since none of the so called "atmospheric" or cold tubes utilize a jacketed tube, all must be inclined or vertical instead of level so that gravity helps with the condensate disposal, or, if the tubes are level, the headers must be angled to promote drainage. This results in an apparatus that is more bulky and difficult to install. In some cases, the less efficient use of the cross section of the duct or air handler can result in unwanted loss of distribution surface. Other systems use "fenders" or structures that insulate the cold tube from the air stream in an attempt to keep the dispersion tube at a temperature higher than that of the air stream. These structures also take up space in the duct. Furthermore, these systems usually disperse steam downstream which accelerates the steam and lengthens the vapor trail. Such systems also usually include special nozzles in the orifices of the dispersion tube to permit steam to escape while preventing the escape of condensate.
A jacketed dispersion tube system of the prior art is illustrated in FIG. 1. The humidification system has a source of steam S which is connected by piping to a jacket J at point A in the Figure. The jacket J is internally baffled so that steam is forced to the outboard end of the jacket and then flow is reversed, the steam flowing back towards the separator R where the steam/condensate exits the tube at point B and is forced into the separator R at point C. The separator R performs a function of letting the condensate run to the steam trap, while the dry steam rises and sits against the valve V. The entire device stays hot, ready for the inflow of steam through the valve V when the humidistat calls for humidity.
When the valve V is opened, steam enters the injection tube T and flows along the tube T to the closed end E opposite the valve. Steam escapes from the tube T through the orifices O. There is no provision for collecting condensate from the tube T, it being assumed that all condensate is removed from the steam by the separator R and that little condensate is formed in the tube T because the jacket J keeps the temperature of the tube T at or near steam temperature.
FIG. 2 shows another prior art jacketed system with more than one tube. Multiple tubes are used in larger ducts or air handlers to promote the release of steam into as much of the air stream as possible, thereby shortening the vapor trail. The principal of operation is the same as a single tube except that two sources of steam, S1 and S2 are used. One source S1 feeds the separator R and the source S2 is limited to tube heating. Because more condensate is created by the extra tubes, isolating the jacket line and trapping it separately is very useful.
A variation on the hot-jacketed system is seen in U.S. Pat. No. 4,265,840 (Bahler). Here, an outer chamber 6 is connected to the steam supply pipe 1. Steam enters the outer chamber 6 and then flows into an inner chamber 7. Steam exits the system through inlet openings 10 communicating with the inner chamber 7 and outlet elements 11 communicating with the environment. Condensate 13 which accumulates on the walls of the outer chamber 6 drains back along these walls to the steam supply pipe 1. In a variation shown in FIG. 2, both the inner chamber 7 and the outer chamber 6 communicate with the steam supply pipe 1.
A problem with the Bahler system is that the walls of the inner chamber 7 are spaced from the walls of the outer chamber 6, which creates a dead space for condensate 13 to accumulate. The walls of the outer chamber 6 will always be exposed to the cool air stream 2, and as can be seen in the patent, condensate will form along these walls. Further, this spacing creates a longer path for steam to travel through the openings 10, 11 than in the system described in the current patent application, so that additional condensate may form. The unjacketed collector 1 will also be exposed to the cool air stream and will produce condensate which will blow into the dispersion tube. Also, condensate coming from the dispersion tube will drip into the collector and be recycled into the dispersion tube, because the steam supply header is not separate from the collector. As a result of these problems, it is impossible for the Bahler device to be mounted completely horizontally in the duct. Rather, Bahler depends on gravity to drain condensate out of the outer chamber 6.
An earlier cold tube system is illustrated by U.S. Pat. No. 5,126,080 (Morton). In the Morton patent, a plurality of elongate dispersion tubes are mounted vertically within a duct, or at least not substantially horizontally, so that one end of each tube is higher than the other end, thus promoting drainage of condensate by gravity. The tubes are cold at all times, without a pre-heated jacket. As soon as the steam control valve opens, hot steam will hit the cold dispersion tubes and immediately form condensate. The tubes have internal structure which attempts to force the condensate to drain along the walls of the tube, rather than spitting out through the orifices of the tubes. To promote this, a plurality of vapor nozzles are mounted within the dispersion tube orifices, with the nozzles protruding well inwardly of the inside walls of the tube. As a result, condensate will adhere to the inside surfaces of the tubes and drain downwardly along the inside surface.
To further promote drainage of condensate, both the supply header and the return header in the Morton patent must be tilted at an angle to the horizontal. This produces a bulky installation that takes up expensive space within the duct. A completely horizontal installation of the tubes is not possible.
There is a need for a steam dispersion device that is normally cold (unheated) in periods between humidification, but that rapidly reaches the temperature of live steam when steam is introduced into the dispersion device and wherein the temperature of the dispersion device is maintained at or near steam temperature without the need for a pre-heated jacket surrounding the dispersion tube.
There is also a need for a steam dispersion device that rapidly carries away any condensate that does form in the dispersion tube without the need for the dispersion tube to be tilted at an angle to the horizontal and without the need for supply and return headers to be tilted from the horizontal.